1. Field of the Invention
This invention relates generally to automated printing machines and, more particularly, to an improved automated printing machine and process for printing by silk screening in one or more colors on material carried on elevated pallets secured to an endless belt drive, having a positively indexed drive for moving the elevated pallets into and out of printing and drying stations, without hard stops.
2. Description of Prior Art
As is well known, many types of materials and products may be printed on utilizing what is referred to as stenciling or silk screening. Many printing applications, such as the silk screening of printed circuits, or intricate designs having a multiple of colors, require a high degree of precision. To provide the necessary precision in known printing machines, mechanical indexing mechanisms have been utilized to align a pallet carrying a workpiece to be printed on, with the silk screen printing mechanism. In automated machines having more than one print station, to perform such silk screen printing, pallets carrying workpieces to be printed are normally moved by an endless belt through the printing station. In order, for example, to accurately print in more than one color on the workpieces carried by the pallets, the pallets must be stopped, or somehow fixed in relationship to an indexing drive mechanism, to ensure accurate placement of the workpiece from one print station to the next. This indexing is usually carried out by mechanical means, or electro-mechanical means utilizing rigid mechanical connections.
One such known silk screen printing machine using an endless belt-type drive, is shown in U.S. Pat. No. Re. 29,160 to Jaffa, which discloses an oval track rail with a series of pallets supporting workpieces moved in a horizontal plane radially about a vertical axis. The pallets are mechanically indexed from station to station. A printing head assembly is operatively associated for movement into and out of printing relationship with one or more of the pallets as the pallets are mechanically indexed and maintained in the horizontal plane. This patent also discloses the use of one or more locating bars, which mechanically cooperate with the pallets to ensure proper registration of the pallets when in the printing position, and indexing means associated with the drive means in the form of a ram-stop cooperating with a cam follower, to effect intermittent indexing of the pallets from station to station, during machine operation.
Various other U.S. Pat. Nos. such as 4,054,091 to Bradley, 4,063,503 to Ichinose, 4,079,674 to Ichinose, 4,273,042 to Machida, 4,404,903 to Cronin, 4,474,109 to Yara, 4,712,474 to Motev, 4,735,139 to Szarka, 4,819,559 to Szarka, and 5,327,827 to Richardson disclose other automated or mechanical printing processes, some of which drive and index printing pallets, or mechanical printing apparatus which attempt to solve the precision alignment or known problems, as indicated therein. Some of these patents include heating booths, drying means, washing means, or the like to dry printed items and to wash printing surfaces. None of these patents, however, disclose an automated printing machine which provides multiple printing stations, for printing in one or more colors, integrated drying means, so as to provide complete, accurate, automated printing and drying of larger, more complex pieces with more positive indexing, and which is not subject to mechanical failure because of hard stops.
Therefore, although the known printing processes and machines shown in the prior art solve many of the problems with precision printing of some workpieces, and attempt to solve the problems that occur because of the stretching of endless belts and/or hard stopping required with known mechanical indexing means, none of the available processes or machines solve all the known problems with precision alignment, or enable an automated printing machine to more accurately and efficiently print large size pieces, in one or more colors, at higher Speeds, while being positively indexed in a more desirable manner.